Cell-substrate adhesion of cells derived from mouse mammary carcinomas and normal glands has been examined by measurement of the ease of detachment of cells. A number of detachment protocols were tested; a protocol involving treatment with a divalent cation chelator was found to be a useful assay system. The normal gland-derived cells became more difficult to detach with increasing time in culture. Some tumor-derived cells were always easier to detach than the normal cells, whereas other tumor-derived cells were initially more difficult to detach than the normal cells but became easier to detach with time. The last pattern may represent an initial strong cell-substratum interaction that is followed by degradation of the external matrix components, i.e., properties that would facilitate metastatic dissemination of cells. Established cell lines derived from mouse mammary carcinomas have also been found to exhibit the two different detachment patterns observed with the primary tumor-derived cells. The detachment properties of these two different cell types have been examined in detail. The tumor cells that are always easy to detach appear to degrade matrix components soon after plating while those tumor cells that are initially difficult to detach do not initially degrade matrix components. The combined findings suggest that in some tumor cells there is regulation of attachment to and degradation of the extracellular matrix. The nature of this regulation is currently under study. (A)